The present invention is directed generally to an improved method and system for determining the actuating pressure of a servo cylinder actuated by pressurized fluid.
DE 199 31 973 A1, which is incorporated herein by reference, discloses a device for controlling a servo assembly for a manual shift gearbox for a motor vehicle. The servo assembly is provided with two servo cylinders operated by pressurized fluid, e.g., hydraulic fluid. The cylinders actuate a gearbox actuating element, which in conventional manual shift gearboxes is the manual shift lever, in longitudinal and transverse directions.
Selection of gates and gears is possible at the gearbox. The servo cylinder for gate selection is known as the xe2x80x9cgate cylinder;xe2x80x9d the servo cylinder for gear selection is known as the xe2x80x9cgear cylinder.xe2x80x9d
In engaging a gear, it is desired that the gear cylinder be capable of being operated with relatively fine and accurate increments of positional force to ensure that synchronization of the toothed gears of the gearbox, or of the synchronizing rings, is accomplished smoothly and with minimal wear. Because in pressurized fluid operated servo cylinders of the type disclosed in DE 199 31 973 A1 a physical relationship or proportionality exists between the output positional force and the actuating pressure present in the servo cylinder, the area of the piston face of the servo cylinder being the proportionality constant, incremental delivery of positional force can be achieved by incrementing the actuating pressure. For this purpose, it is desirable to determine the actuating pressure of the servo cylinder as accurately as possible.
For cost reasons, and in order to minimize the complexity of the servo assembly, it is generally not desirable to utilize a pressure sensor at the servo cylinder specifically for determination of the actuating pressure. Instead, as disclosed in DE 199 31 973 A1, a pressure sensor located elsewhere, typically upstream of the servo cylinder, is utilized. Depending on the operating position of the valves of the servo assembly, the pressure sensor can detect different pressures, such as the inflow pressure of the pressure supply or a pressure comparable to the actuating pressure of the servo cylinder. However, the further the pressure sensor is from the point where pressure is to be measured, the less accurate the measurement.
It is desired to provide an improved, more accurate approach for determining the actuating pressure of a servo cylinder actuated by pressurized fluid for regulating the actuating pressure of and actuating force output by the servo cylinder based thereon.
Generally speaking, in accordance with the present invention, a method and associated system for determining the actuating pressure of a servo cylinder actuated by pressurized fluid for regulating the actuating pressure of and actuating force output by the servo cylinder based thereon are provided that improves over prior art methods and arrangements.
In a preferred embodiment of the system according to the present invention, the servo cylinder is a double-acting servo cylinder having pressurized fluid inflow and outflow ports for supplying a pair of pressurized fluid chambers. A pump supplies the servo cylinder with pressurized fluid via pressurized fluid lines or conduits. A pair of electromagnetically actuated 3/2-way valves are provided in fluid communication with the servo cylinder. An electromagnetically actuated 2/2-way valve functions as a pressure modulator.
Single-acting servo cylinders having one fluid port and one fluid chamber can also be used in the system according to the present invention.
An electronic control unit is provided to control valve actuation and thereby modulate the fluid pressure and regulate the actuating pressure and output actuating force of the servo cylinder as determined in accordance with the method of the present invention. In vehicle gearbox control applications of the method and system according to the present invention, actuating force curves representing predetermined servo cylinder operation can be programmed into the electronic control unit to facilitate smooth and precise gearbox operation.
In accordance with the method and system of the present invention, the actuating pressure of the servo cylinder, which relates to the positional force of the servo cylinder, can be determined with a high degree of accuracy and with minimal computational effort by using the positional displacement of the servo cylinder, a value that is necessary in any case for servo cylinder controllers. The positional displacement can be obtained from an existing source, such as from a displacement sensor integrated into the servo cylinder or mounted externally. Alternatively, the positional displacement can be obtained from a device connected to the servo cylinder, for example, a gearbox provided with a displacement sensor, that is capable of transmitting the displacement information, e.g., over a data bus, to a control device such as the electronic control unit.
A pressure sensor provided for measuring the inflow pressure is desirably located along the pressurized fluid line leading to the servo cylinder at a point that is upstream of the extended servo cylinder proximate to the pressure outlet of the electromagnetically actuated 2/2-way valve. At this location, a higher pressure level is present at the pressure sensor than in the servo cylinder, as the line leading to the servo cylinder causes pressure loss. By virtue of the higher pressure level at the pressure sensor, a higher signal resolution and a more accurate pressure reading is possible than could be obtained by sensing pressure directly at the servo cylinder.
A value representing the flow velocity of pressurized fluid through the line can be determined from the positional displacement of the servo cylinder or from the change of positional displacement. This can be accomplished by differentiation of the positional displacement with respect to time. In systems where time is measured digitally, the change of positional displacement can be computed by means of difference ratios.
The temperature effect, which influences the density of the pressurized fluid, can also be taken into consideration. For example, based on the temperature of the pressurized fluid measured using a temperature sensor, a corrected density of the pressurized fluid as a function of the temperature can be computed.
Accordingly, it is an object of the present invention to provide a method and associated system capable of determining the actuating pressure of a servo cylinder with a high degree of accuracy and minimal computational effort.
It is an additional object of the present invention to provide a method and system for regulating the actuating pressure of and actuating force output by a servo cylinder to enable the operation of a motor vehicle gear cylinder with fine and accurate increments of positional force.
It is also an object of the present invention to provide a method and system for determining the actuating pressure of a servo cylinder for regulating the actuating pressure of and actuating force output by the servo cylinder based thereon that is cost effective and minimizes instrumental complexity.
It is another object of the present invention to provide a method and system for determining the actuating pressure of and actuating force output by a servo cylinder that senses different pressure values utilizing one pressure sensor.
It is a further object of the present invention to provide a method and system for determining the actuating pressure of and actuating force output by a servo cylinder that takes into consideration the positional displacement of the servo cylinder.
It is a still further object of the present invention to provide a method and system for determining the actuating pressure of and actuating force output by a servo cylinder that takes into consideration the temperature of the pressurized fluid.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention accordingly comprises the various steps and the relation of one or more of such steps with respect to each of the others, and embodies features of construction, combinations of elements, and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.